Method and apparatus for manual delivery of volume and pressure-control artificial ventilation

ABSTRACT

A combination of a bellows structure ( 12 ), volume restrictor, and pressure restrictor for use on a hand-operated resuscitator is provided to enable delivery of ventilation within specific volume and pressure limitations specified by the operator. The bellows structure ( 12 ) consistently provides predictable and uniform generation of gas flow for ventilation without regard to one or two-handed technique, hand placement, or hand size. The volume restrictor, primarily comprising of an inflow obturator ( 20 ), outflow obturator ( 22 ), and placement cam ( 34 ), enables the physician to specify a specific tidal volume to be delivered, which constitutes a volume-controlled cycling capability of the invention. The pressure restrictor, primarily comprising of an outer housing ( 40 ), stopper housings ( 41 ), and a stopper ( 50 ), enables the physician to specify a specific maximum airway pressure to be exposed to the patient, which constitutes a pressure-controlled cycling capability of the invention. Combined use of the volume and pressure restricting mechanisms can provide for various additional abilities, including limiting airway pressure during volume-controlled ventilation or providing a means to detect decreasing pulmonary compliance.

This application claims priority under 35 U.S.C. § 119 (e) from U.S.patent application Ser. No. 10/055,562, filed Jan. 23, 2002, entitledMethod and Apparatus for Manual Delivery of Volume and Pressure-ControlArtificial Ventilation, which is based upon U.S. Provisional ApplicationNo. 60/263,426, filed Jan. 23, 2001, entitled Method and Apparatus forManual Positive Pressure Delivery of Metered Artificial Ventilation.

BACKGROUND OF THE INVENTION

The following invention pertains to the art of manually providingpositive-pressure artificial ventilation to the non-breathing patient,and particularly to patients suffering acute respiratory and/orcardiopulmonary arrest.

The critical role of the lungs in maintaining life is well known—mostindividuals are aware of the body's need for oxygen to maintain cellularmetabolism and recognize the critical role of the lungs in providing thenecessary amounts of oxygen to support life. When breathing stops, as itdoes during cardiac arrest, a vicious circle of events take place as thecells of the body attempt to survive without oxygen necessary formetabolism. These events constitute the initial phase of biologicaldeath, which rapidly progresses without prompt emergency treatment.

Accordingly, one of the first priorities in resuscitation is toestablish a means to provide artificial ventilation to a patient. Thisbegins with what is known in the art as establishing an airway, which isthe process of providing an open passage for air to travel through thepatient's mouth, throat, and trachea (or windpipe) to the lungs. Thiscan initially be achieved by properly positioning the patient's head andneck.

Once an airway is established, one next provides artificial ventilationby forcing air into the patient's mouth, through the trachea, and intothe lungs. When utilizing the mouth-to-mouth method of ventilation, noventilatory device is used. This is the form of artificial breathingtaught by the American Heart Association and the European ResuscitationCouncil as part of Basic Life Support (BLS) courses on cardiopulmonaryresuscitation (CPR). However, healthcare professionals, both in-hospital(physicians, respiratory therapists, nurses, etc.) and pre-hospital(emergency medical technicians, paramedics) most often use variousmedical devices to provide artificial ventilation. These can includepocket masks (through which the rescuer manually blows to inflate thepatient's lungs), demand valves (a mechanical device which inflates thepatient's lungs with compressed oxygen when a button is manually pressedon the face mask), and automatic transport ventilators (fully automaticmechanical ventilators which deliver sequential breaths to the patient),however the device which is most frequently employed is the manualresuscitator.

Also known as an “Ambu bag” or “bag-vale-mask” (BVM), the manualresuscitator is a balloon-type device frequently portrayed on fictionalor documentary medical television programs. Essentially a hand-poweredair pump, the device consists of a squeezable, randomly pliableself-inflating bag (or fluid chamber) which, when squeezed by theoperator, displaces air from the bag and out a port to which a face maskcan be connected. More specifically, the technique to use a manualresuscitator comprises utilizing one hand to perform the combined taskof maintaining proper positioning of the head (to maintain the airway),while applying pressure on the mask to form a seal between the patient'sface and the mask. At the same time, the operator uses the free hand tosqueeze the fluid chamber and thus displace air into the patient's lungsunder positive pressure. When the fluid chamber is released the patientpassively exhales, while the fluid chamber returns to its natural,inflated state in preparation for the next breath.

The manual resuscitator was originally designed in the 1930 's, and overthe years has fortified its position as the first-line device employedin artificial ventilation. The balloon-type design is inherentlyintuitive—little training is required to learn how to operate thedevice, and its simplicity makes it ideal for use in franticenvironments commonly associated with resuscitation efforts. Its simpledesign also makes it inherently reliable—another highly desirableattribute for a medical device essential for resuscitation. Finally, thecost of manual resuscitators is very low, making it possible for them tobe stored in readiness in highly accessible places throughout thehospital.

With these strong attributes intrinsic to the basic design of the manualresuscitator, little has been done over the years to modify it.Improvements have included utilization of new materials in theconstruction of the squeezable fluid chamber to facilitate a better,more comfortable grip. Other design refinements have decreased weightand decreased manufacturing cost, further contributing to the economy ofdisposable versions of the device.

Particularly during the past two decades, however, a number ofadvancements in medicine have greatly contributed to the understandingof pulmonary physiology and the pathophysiology of cardiorespiratoryarrest. These advancements inspired additional clinical studies tospecifically assess the performance of manual resuscitators, which havesince been proven to have grave inadequacies.

One of the first problems identified was a general inability for singlerescuers to simultaneously use one hand to maintain the face mask seal,use the other hand to squeeze the chamber, and generate a breath ofsufficient volume (called the tidal volume). One reason for these lowvolumes is it is difficult to maintain an airtight seal between the facemask and the patient's face with one hand, resulting in frequent loss ofa significant portion of the tidal volume to leakage. Another problemcontributing to small tidal volumes is the randomly pliable nature ofthe skin of the fluid chamber of the device. When squeezed, areas not indirect contact with the rescuer's hand bulge out, reducing theefficiency of the manual compressing action which constitutes operationof the device. Other studies proved these deficiencies were not relatedto the level of training of the rescuer—paramedics, nurses, andphysicians operating the device were all found to be unable toconsistently provide ventilation at recommended levels. While it mayseem obvious this problem can be overcome simply by providing morefrequent breaths, this strategy can actually result in further decreasedventilation to the patient.

This apparent paradox, where increasing ventilatory rate may actuallylead to decreased overall ventilation of the lungs, is related to aphysiologic principle known as anatomic deadspace. The actual exchangeof gases in the lungs, called respiration, occurs in tiny air sackswhich are surrounded by a web of blood capillaries. These sacks, calledalveoli, is where the blood receives oxygen from the air inhaled inexchange for carbon dioxide waste, which is exhaled. In everyindividual, a significant portion of a given breath remains in themouth, throat, trachea, and the various distal airways in the lungs,which are collectively referred to as deadspace. Residual air occupyingdeadspace at the end of inhalation never actually reach the alveoli andtherefore do not contribute to gas exchange. Accordingly, sincedeadspace is an anatomic constant unaffected by the size of the breathadministered, when small breaths are given deadspace negates 25-35% theof total tidal volume delivered, whereas if large breaths are givendeadspace consumes only 10-20% of each tidal volume. Consequently, oneventilating rapidly but with small tidal volumes is likely to deliverless effective ventilation than one would by utilizing a larger tidalvolume at a slower rate.

This paradox has significant clinical implications. Frequently duringresuscitation, certain blood tests are performed which measures theamount of oxygen and carbon dioxide in the blood. When such examinationsreveal decreased oxygen levels or, more importantly, elevated amounts ofcarbon dioxide in the blood, the individual ventilating is usuallyprompted to provide increase their efforts. The natural response wouldbe to increase the ventilatory rate, however, higher ventilatory rateshave been associated with increased operator hand fatigue andinattentiveness. Consequently, tidal volumes have been observed todecrease as ventilatory rates increase. Therefore, despite increasedventilatory rate (and operator impression they are providing improvedventilation), overall ventilatory effectiveness may actually decrease,because as tidal volume decreases anatomic deadspace representsincreasing proportions of each breath, which can provide a greaternegative affect on alveolar ventilation than the positive effect of ahigher rate.

This concept is not universally recognized among health care providers.As a result, many continue to inappropriately regard the effectivenessof the manual resuscitator as rate-dependent rather thanvolume-dependent.

Pursuant to findings demonstrating inability of single rescuers togenerate adequate volumes, authoritative agencies recommendedimplementation of a two-person technique to utilize manualresuscitators—one-person to maintain a face mask seal with two hands,while the other rescuer squeezes the fluid chamber using two hands.Clinical studies performed thereafter sought to document delivery ofhigher tidal volumes consistent with resuscitation standards.

While increased volumes are produced by the two-person technique,clinical studies also identified significant hazards associated with thetwo-person technique. To compensate for the aforementioned bulging-outphenomenon during the one-handed technique, resuscitator manufacturersmake fluid chambers disproportionally large. Thus when two hands areused to provide a breath, improved surface-area contact between thehands and the fluid chamber decrease the extent of outward bulging,resulting in the generation of excessive volumes, air flow rates, andairway pressures.

Generation of excessive volumes, pressures, and flow rates has beenshown to cause significant hazards to the patient. One study inparticular assessed the distribution of gas between the lungs andstomach in patients ventilated with manual resuscitators. Even with theone-person technique, air flow rates and airway pressures were excessiveenough to cause air to preferentially enter the stomach, and at times,flow to the stomach actually was greater than the amount received by thelungs. Inflation of the stomach with air (called gastric insufflation)markedly increases the risk of patient vomiting, potentially resultingin stomach contents entering the lungs (a grave complication). In fact,the danger and incidence of gastric distention associated with the useof prior art manual resuscitators has recently been determined to begreat enough to recommend utilization of child-size versions of theprior art on adult patients, since the smaller size of the child deviceprovides a safeguard against generation of excessive volumes, pressures,and flow rates which leads to a decreased incidence of thiscomplication. Accordingly, some resuscitation authorities nowrecommended that, in lieu of a truly safe and effective ventilatoryadjunct, when ventilating an adult with the prior art it is preferableto compromise ventilatory effectiveness in order to achieve greatersecurity from complications associated with adult-versions of thedevice.

Other measures can be employed to palliate these deficiencies of theprior art. A more definitive form of airway control involves placementof a tube (called an endotracheal tube) directly into the patient'strachea, thus isolating the airway from the gastrointestional tract.After intubation, the face mask can be detached and the manualresuscitator directly connected to a port on the endotracheal tube. Thisobviates the need for active airway maintenance, provides definitiveairway protection, and allows a single rescuer to use two hands toventilate the patient.

However, endotracheal intubation is a medical procedure requiringconsiderable skill and experience and is usually performed by aphysician, respiratory therapist, or nurse anesthetist. When performedsuccessfully on the first attempt intubation can be completed in lessthan 10 seconds; however, the procedure is often successful only aftermultiple attempts, spanned over several minutes. Indeed, at timesintubation attempts are all unsuccessful on a particular patient,perhaps due to trauma, anatomic aberrancies, and/or inexperience of theindividual attempting to perform the procedure. Until the patient issuccessfully intubated, the aforementioned deficiencies of the prior artcontinue to jeopardize patient survival.

Even after successful intubation, additional studies have shown use ofprior art manual resuscitators are still associated with significantrisks. As previously indicated, one-handed operation results ininadequate ventilation to the patient, while two-handed operation isassociated with excessive volumes, flow rates, and pressures.

One-handed operation in the intubated patient continues to result inventilatory volumes which decrease the ability of the lungs to provideoxygen to the blood. More importantly, this also affects the amount ofcarbon dioxide waste the lungs can remove from the blood, which is alsoan absolute requirement for the sustainment of life. Carbon dioxide iscreated as a by-product of metabolism, and the accumulation of excessiveamounts in the blood, called hypercarbia, causes an acidic pH of theblood which has various negative affects on the body. Research hasdefinitively shown hypercarbia has several potent effects on the heartwhich directly contributes to decreased patient survival from cardiacarrest. Hypercarbia has been shown to increase the tendency of the heartto degenerate into a chaotic arrhythmia called ventricular fibrillation,where the heart muscle essentially quivers and produces no pumpingaction. Additionally hypercarbia has been demonstrated to supportsustainment of ventricular fibrillation, and cause it to recur after anormal rhythm has been successfully restored. Finally, significantdecreases in the effectiveness of electrical defibrillation (thetreatment for ventricular fibrillation) has proven to be directlyrelated to the presence of hypercarbia. Even in normal, beating tissue,hypercarbia has been demonstrated to immediately decrease the pumpingstrength of heart muscle. The only way to control hypercarbia, and thusoppose these potent effects on the heart, is to provide effectiveventilation to the patient. Accordingly, since one-handed operation hasbeen shown to generate inadequate volumes to both intubated andunintubated patients, it would appear its employment duringresuscitation may contribute to patient mortality.

However, employing a two-handed technique in the intubated patient,while preventing the harmful effects of hypoventilation and hypercarbia,are associated with the aforementioned risks due to generation ofexcessive tidal volumes, airway pressures, and flow rates othersignificant risks. The potential for lung injury is more pronounced whenthe patient is intubated since, under these circumstances, theendotracheal tube provides a sealed, direct connection between themanual resuscitator and the patient's lungs. Accordingly, excessive orover-aggressive ventilatory techniques, encouraged in-part by theintense environment of frantic resuscitation efforts, have beendocumented to cause traumatic injury to the lungs, particularly inpediatric and elderly patients.

In patients who are successfully resuscitated, high inflation pressureshave been shown to be a contributing factor to the development of theAcute Respiratory Distress Syndrome (ARDS), the treatment of whichrequires sustained mechanical ventilation and intensive-carehospitalization over several weeks or months. Treatment of ARDS isextensive, extremely costly, and frequently unsuccessful. Excessiveventilatory volumes and pressures can also cause acute life-threateninglung injury through actual disruption of lung tissue. In addition topneumothorax (collapsed lung), there have been several reports of caseswhere high inflation pressures generated by manual resuscitators havecaused air to directly enter the bloodstream (called an air embolism), acomplication which is almost invariably fatal. Even in patients with aperfusing rhythm, high airway pressures are known to decrease bloodpressure, cardiac output, and oxygen delivery significantly by causingthe lungs, inflated with high pressures, to compress the heart and thelarge blood vessels in the chest.

Another deficiency of the prior art is related to high variability oftidal volumes generated by the device. Small changes in hand position onthe fluid chamber are exaggerated by the bulging-out effect, causingdisproportionate changes in tidal volumes. This attribute contributes tothe inability of the prior art device to provide consistent andpredictable ventilation to the patient, regardless of operatortechnique. This has been postulated to interfere with the ability tointerpret certain blood tests which assess the effectiveness ofventilation and which are fundamental measures of ventilationeffectiveness.

Another disadvantage associated with breath-to-breath inconsistency isan inability to detect certain life-threatening conditions which areassociated with increasing lung resistance. The presence of alife-threatening lung injury (e.g., tension pneumothorax) may bedetected early by noticing a requirement for progressively increasingventilatory pressures to achieve delivery of a specific tidal volume.With marked breath-to-breath variation associated with the prior art,this condition is likely to be apparent only after advanced progressionof the injury begins to contribute to circulatory collapse andappearance of other ominous physical findings. Late identification ofsuch underlying injuries further jeopardizes the patient and complicatestreatment.

Another challenge in resuscitation is monitoring placement of theendotracheal tube. The trachea, after it descends from the throat,bifurcates into two main branches each of which go to one of the twolungs. The first concern with the placement of the endotracheal tube isto be sure it has been positioned in the trachea instead of theesophagus (which leads to the stomach). While several techniques todetect carbon dioxide (which is not present in quantity in the stomach)provides assurance the tube has been placed in the trachea, aside frominterrupting resuscitation to obtain a chest X-ray there is no way toreadily assess exact placement of the endotracheal tube within thetrachea. This is a significant concern; if the tube is advanced ordisplaced too far, the end of the tube may progress beyond thebifurcation and thus only one lung will be ventilated (probablyresulting in patient death if not recognized). Due to the aforementionedbreath-to-breath variability of the prior art, this condition, alsomarked by increased pressures associated with the delivery of a specificvolume, is not likely to be obvious via the operation of the prior art.

Accordingly, one can see the prior art manual resuscitator, while simpleand inexpensive in design and operation, has multiple barriers to theconsistent delivery of safe and effective artificial ventilation. Itsuse in unintubated patients either results in inadequate ventilation andhypercarbia with the one-person technique (or if a child-size device isemployed), or the unacceptable risk of gastric insufflation andaspiration of vomitus associated with the two-person technique with thefull-sized adult device. When used on intubated patients employment of aone-handed technique contributes to hypoventilation and hypercarbia, thelatter of which has been proven to have several potent affects on theheart which directly contribute to increased mortality from cardiacarrest. When two-handed operation is used on intubated patients, thelack of an ability to guard against the generation of excessive airwaypressures and volumes has been demonstrated to result in circulatorydepression and a significant incidence of lung injury, the latter ofwhich results in further complications, increased hospitalization,and/or death. Furthermore, breath-to-breath variability associated withthe prior art results in unpredictable and inconsistent ventilation(affecting the ability to interpret certain blood tests), and decreasesor inhibits the sensitivity for one to detect progressively increasingpulmonary resistance to ventilation, which can be indicative ofendotracheal tube displacement or the presence of underlyinglife-threatening intrathoracic injury.

Thus, it can be seen there is a need for a device which sharesbeneficial attributes of the prior art (simplicity, reliability,affordability, and disposability) while offering new capabilities whichaddress the several performance inadequacies which have been proventhrough clinical studies. There is a need for a device which can guardagainst the hazards associated with hypoventilation and hypercarbia byconsistently providing predictable volumes of air without regard forhand placement, the size of a rescuer's hands, or the number of handsemployed for operation. There is a need for a device which can providesafeguards against the generation of excessive volumes and airwaypressures which have been demonstrated to contribute to gastricinsufflation, circulatory depression, complications, extendedhospitalization, and fatal lung injury. Finally, there is a need for adevice which can decrease breath-to-breath variability in volume tofacilitate a predictable level of artificial ventilatory support, enablemore accurate interpretation of blood test results, and contribute toearly identification of decreased lung compliance secondary tolife-threatening intrathoracic injury or clinically significantdisplacement of an endotracheal tube.

SUMMARY OF THE INVENTION

In accordance with the present invention an improved design for a manualresuscitator is provided comprising a bellows incorporated into thesqueezable fluid chamber which prevents outward bulging of the bagduring operation, a volume restrictor which enables the operator topre-select a specific tidal volume to be delivered with each breath, anda pressure restrictor which enables the operator to pre-select aspecific maximum airway pressure to which the patient will be exposed.

Several objects and advantages of the invention are:

-   -   (a) to provide a bellows which enables uniform and predictable        compression of the fluid chamber without regard to hand        placement, size of the operator's hands, or use of one or two        hands for operation;    -   (b) to provide variable rates of air displacement depending on        the volume delivered, whereby smaller volumes intended for        infants and pediatric patients require a greater relative        movement of the bellows (thus providing more precision) compared        to larger volumes provided to adult patients;    -   (d) to provide a ramped flow rate when used on adult patients,        whereby low flow rates are provided at the beginning of a breath        and slowly increase toward end-inspiration, which improves        distribution of gas in the lung;    -   (e) to consistently provide full, effective, and uniform tidal        volumes without regard to technique, thus allowing a physician        to prescribe a specific and predictable degree of ventilatory        support tailored to the patient's specific physical attributes        and underlying illness;    -   (f) to provide safeguards to prevent patient harm caused by the        delivery of excessive tidal volumes, airway pressures, and flow        rates;    -   (g) to enable assertive delivery of large tidal volumes without        jeopardizing patient safety, thus providing safer, more        effective ventilation;    -   (h) to provide consistent volumes with each breath, increasing        the uniformity of airway pressures sensed by the operator and        accordingly the ability to detect progressively increasing        airway resistance, which also increases the clinical        applicability of certain monitoring tests;    -   (i) to provide an ability to prescribe a specific maximum airway        pressure to which the patient will be exposed;    -   (k) to enable adequate tidal volumes to be administered to        unintubated patients at low airway pressures, thus decreasing        the incidence and significance of gastric insufflation and risk        to the unprotected airway;    -   (l) to provide a new ability to detect progressively increasing        airway pressure by combining the use of both volume and pressure        safeguard mechanisms;    -   (m) to provide an improved ability to detect underlying        intrathoracic injuries and/or a displaced endotracheal tube        through detection of decreasing pulmonary compliance;

Further objects and advantages will become apparent upon considerationof the drawings and detailed description of the invention.

DESCRIPTION OF THE DRAWINGS

In FIGS. 1 a-c of the drawing figures an example embodiment of acylindrically-shaped bellows is shown. FIG. 1 a shows the bellows in afilly inflated condition, FIG. 1 b shows bellows in a partially inflatedcondition, and FIG. 1 c illustrates the bellows in the deflatedcondition.

FIGS. 2 a-d shows components of an example embodiment of a volumerestrictor. FIG. 2 a shows a cone-shaped inflow obturator which containsa number of inflow fluid conduits to enable flow of fluid through theresuscitator. FIG. 2 b shows a donut-shaped inflow obturator spacer withan opening or lumen in the center to permit fluid flow. FIG. 2 c shows acombination cone-shaped inflow obturator together with the inflowobturator spacer, the two of which may be permanently joined into asingle component. FIG. 2 d shows an outflow obturator, which, other thanorientation, is identical to the inflow obturator.

FIG. 3 a-c shows additional components of another example embodiment ofa volume restrictor. FIG. 3 a shows a disk-shaped placement selector,which contains numerous fluid conduits to permit fluid flow. FIG. 3 bshows a ring-shaped inflow selector spacer, and FIG. 3 c shows these twocomponents assembled together with the addition of a placement cam, allthree of which form a single assembly.

FIG. 4 a-c shows sequential assembly of the invention, including allcomponents of the example embodiment of the volume restrictor. FIG. 4 ademonstrates how the inflow and outflow obturators are positioned ontothe placement cam. FIG. 4 b shows complete assembly of the volumerestrictor. FIG. 4 c shows the combined assembly of the volumerestrictor and the example embodiment of the bellows, with the additionof a fluid chamber skin.

FIG. 5 a shows the invention in a fully inflated condition with thevolume restrictor set at the maximum allowable volume. FIG. 5 b showsthe bellows in the fully deflated condition, whereby the obturators arepositioned as to not interfere with full compression of the bellows.

FIG. 6 b shows the invention whereby the volume restrictor has beenadjusted to provide delivery of a reduced volumes. FIG. 6 a provides acomparison view of the volume restrictor in the position to providefull, unimpeded volume delivery.

FIG. 7 a shows the invention in the same condition of FIG. 6 b, wherebythe volume restrictor is positioned to provide for reduced volumedelivery. FIG. 7 b shows how compression of the bellows is now partiallyimpeded by the obturators of the volume restrictor, resulting in aresidual volume inside the fluid chamber of the bellows atend-inspiration.

FIG. 8 a shows an example embodiment of a pressure restrictor,consisting of an outer housing and internal housing fluid conduits topermit the flow of fluid through the housing. FIG. 8 b shows theorientation and structure of these components from a side view.

FIG. 9 a-b shows a propeller-shaped stopper, which when placed adjacentto the pressure restrictor housing, provides for selective fluid flowthrough the housing based on the rotational position of the stopper.

FIG. 10 a shows the combined outer housing and stopper of the exampleembodiment of a pressure restrictor, whereby the stopper is oriented ina position to permit fluid flow through the housing via the housingfluid conduits, which are unobstructed. In FIG. 10 b, the stopper isdepicted in a rotational orientation whereby the stopper obstructs thehousing fluid conduits, thus interrupting fluid flow through thepressure restrictor. FIG. 10 a-b also shows an example embodiment of acontroller of the pressure restrictor which employs a compressiblespring which surrounds the outer housing of the pressure restrictor.

FIG. 11 a-b demonstrates the same variable positions of the stopperdepicted in FIG. 10 a-b. However, in FIG. 11 a-b the pressure restrictorcontroller has been adjusted to a position which provides greatercompression of the controller spring, changing the operational dynamicsof the pressure-controller.

REFERENCE NUMERALS IN DRAWINGS Bellows Components 10 structural member12 bellows structure 14 bellows structure exterior surface 16 bellowsstructure interior surface 18 fluid chamber Volume Restrictor Components20 inflow obturator 20a inflow obturator center bore 21 inflow obturatorfluid conduit 22 outflow obturator 22a outflow obturator center bore 23outflow obturator fluid conduit 24 inflow obturator spacer 25 inflowobturator spacer lumen 30 placement selector 31 placement selector fluidconduit 32 inflow selector spacer 33 inflow selector spacer lumen 34placement cam Pressure Restrictor Components 40 outer housing 41 stopperhousing 42 housing fluid conduits 43 stopper notch 44 controller channel45 pressure channel 50 stopper 51 pressure header spar 52 pressureheader 53 controller header spar 54 controller header 60 controllerspring 61 stopper header 62 level header 63 controller level 64open-point stop 65 closed-point stop Other Components 77 inflow one-wayvalve 88 outflow one-way valve 99 bellows skin

DESCRIPTION OF THE INVENTION

In FIG. 1 an example embodiment of a bellows is depicted. A plurity ofrectangular structural members 10 can be seen to be coupled togetheralong their long axis, whereby the combination of all the attachedstructural members can collectively be regarded as a bellows structure12. The bellows structure 12 is preferably formed into a cylindricalshape by wrapping the bellows structure 12 into a circular shape alongthe bellows short axis. This shape enables identification of an interiorsurface 16 of the bellows structure and an exterior surface 14 of thebellows structure 12. The three-dimensional space contained by thebellows structure interior surface 16 can constitute a fluid chamber 18of a particular definitive volume. In this example embodiment, thecoupling of the bellows structural members 10 is provided along thoseedges which meet along the bellows structure interior surface 16.Accordingly, adjacent structural members 10 may flex in a directiontoward the interior of the bellows structure 12, providing for a concavecurvature of the bellows structure interior surface 16 and a convexcurvature of the bellows structure exterior surface 14. Conversely, thiscoupling of adjacent structural members 10 does not provide for flexingin a direction outward from the bellows structure 12, which wouldrequire a concave curvature of the bellows structure exterior surface14, because this would necessarily have to result from a convexcurvature along the bellows structure interior surface 16, which is notpossible since this would require separation of coupled edges ofadjacent structural members 10. Accordingly, in FIG. 1 b the bellowsstructure 12 can be seen to be in a partially inflated condition,whereby the fluid chamber 18 is of a diminished volume compared to thevolume of that depicted in FIG. 1 a. Since outward flexing of theadjacent structural members 10 is prevented by the aforementionedcoupling, an application of a compressing force on the bellows structureexterior surface 14 will result in a transition of the bellows structure12 from the fully inflated condition in FIG. 1 a to the partiallyinflated condition depicted in FIG. 1 b. Sustained application of such aforce will eventually result in transition of the bellows structure tothe end-point condition depicted in FIG. 1 c, whereby the bellowsstructure 12 is flattened into an oblong shape in the fully deflatedcondition. In this condition the volume contained by the fluid chamber18 approaches zero. Transition from the deflated condition depicted inFIG. 1 c back to the inflated condition shown in FIG. 1 a can beprovided through a variety of means, including inclusion of an elasticskin lining the bellows structure interior surface 16 and/or theexterior surface 14, or through forced inflation by a fluid underpressure.

FIG. 2 depicts three components associated with an example embodiment ofa volume restrictor designed to be used in conjunction with a bellows ina resuscitator. In FIG. 2 a a substantially cone-shaped inflow obturator20 can be seen, having a number of inflow obturator fluid conduits 21which can be seen to traverse through the cone in a directionperpendicular to the base and parallel to the vertical axis of the cone.These inflow obturator fluid conduits 21 can further be seen to becollectively arranged around the center of the cone in a circularfashion, leaving the outer circumference of the cone free of voids. Inthe actual center of the inflow obturator is a threaded inflow obturatorcenter bore 20 a, which traverses through the inflow obturator in adirection parallel to the inflow obturator fluid conduits 21.

FIG. 2 b depicts an inflow obturator spacer 24 which can be seen to besubstantially disk or puck-shaped. An inflow obturator spacer lumen 25is also shown in the middle of the inflow obturator spacer 24, thecombination of which results in an overall ring or donut-shape of theinflow obturator spacer 24. The dimensions of the inflow obturatorspacer 24 are preferably related to those of the inflow obturator 20depicted in FIG. 2 a, whereby the circumference and diameter of theinflow obturator spacer 24 is equal with that of the base of the inflowobturator 20. Additionally, the diameter of the inflow obturator spacerlumen 25 is sufficiently large enough to encircle the collective groupof inflow obturator fluid conduits 21 which are arranged in a circularfashion around the center axis of the inflow obturator 20. The height ofthe inflow obturator spacer 24 is preferably related to the height ofthe inflow obturator 20, whereby the height of the inflow obturatorspacer 24 is slightly greater than the height of the inflow obturator20. FIG. 2 c depicts the combination inflow obturator 20 and inflowobturator spacer 24 connected along the bases of the two components,whereby the base of the inflow obturator 20 is mated to one of the twoflat-surfaced bases of the inflow obturator spacer 24. The circularcircumference of the inflow obturator spacer 24 is superimposed alongthe same three-dimensional plane of the inflow obturator 20, thusallowing the combination of the inflow obturator fluid conduits 21 andthe inflow obturator spacer lumen 25 to form a straight, continuousfluid passageway which traverses both the inflow obturator 20 and inflowobturator spacer 24.

FIG. 2 d depicts a cone-shaped outflow obturator 22 having outflowobturator fluid conduits 23 and an outflow obturator center bore 22 a,all of which is preferably structurally identical to the inflowobturator 20, inflow obturator fluid conduits 21, and inflow obturatorcenter bore 20 a previously described. In this view the outflowobturator 22 is depicted in an orientation such that the point of thecone-shaped outflow obturator points in a direction opposite to that ofthe inflow obturator depicted in FIGS. 2 a-c.

FIG. 3 a shows a disk-shaped placement selector 30 having a number ofplacement selector fluid conduits 31 which traverse through theplacement selector 30 in a direction perpendicular to the flat bases ofthe placement selector 30. Additionally, the placement selector fluidconduits are arranged in a circular fashion around the center of theplacement selector 30, leaving the outer circumference of the placementselector free of voids. In the actual center of the placement selector30 is a placement selector central bore 30 a which traverses through theplacement selector in a direction parallel to the placement selectorfluid conduits 31. The overall circular diameter and circumference ofthe placement selector 30 is preferably identical to the diameter andcircumference of both the inflow obturator 20 and inflow obturatorspacer 24 depicted in FIGS. 2 a-c.

FIG. 3 b shows a ring-shaped inflow selector spacer 32 having an inflowselector spacer lumen 33. The outer diameter of the inflow selectorspacer is preferably related to the diameter of the inflow obturatorspacer lumen 25 shown in FIGS. 2 b-c, whereby the outer diameter of theinflow selector spacer 32 is slightly less than the diameter of theinflow obturator spacer lumen, so that the inflow selector spacer 32 mayfreely rotate or slide to and fro inward or outward within the inflowobturator spacer lumen 25. The diameter of the inflow selector spacerlumen 33 is preferably related to the placement selector fluid conduits31 and the inflow obturator fluid conduits 21 depicted in FIGS. 2 a-c,whereby the diameter of the inflow selector spacer lumen is sufficientlylarge enough to encircle the collective arrangements of both theplacement selector fluid conduits 31 and inflow obturator fluid conduits21. The height of the inflow selector spacer 32 is preferably related tothe height of the inflow obturator spacer 24 depicted in FIGS. 2 b-c,whereby the height of the inflow selector spacer 32 is slightly greaterthan the height of the inflow obturator spacer 24.

FIG. 3 c depicts the combination of the placement selector 30 and inflowselector spacer 32, whereby one of the two flat bases of the inflowselector spacer 32 is attached to one of the two flat bases of theplacement selector 30, wherein the respective cross-sectional centerpoints of the two components are superimposed alone the sametwo-dimensional plane, thus allowing the combination of the placementselector fluid conduits 31 and the inflow selector spacer lumen 33 toform a straight, continuous fluid passageway which traverses both theplacement selector 30 and inflow selector spacer 33.

Also depicted in FIG. 3 c is a shaft-shaped placement cam 34. The lengthof the placement cam 34 is preferably related to both the length of thebellows structural members 10 (shown in FIG. 1 a-c), the height of theinflow obturator 20 and outflow obturator 22 (shown in FIGS. 2 a-d), theheight of the inflow selector spacer 32, and the height of placementselector 30, wherein the length of the placement cam is equal to thecumulative distance represented by the height of the placement selector30, the height of the inflow selector spacer 32, the height of theinflow obturator 20, the length of the bellows structural members 10,and the height of the outflow obturator 22. The diameter of theplacement cam 34 is slightly less than the diameters of the placementselector center bore 30 a, the inflow obturator center bore 20 a, andthe outflow obturator center bore 22 a. Additionally, the outer surfaceof the placement cam is threaded to mate with the threads of the inflowobturator center bore 20 a. In FIG. 3 c the placement cam can be seen tofit inside the combined placement selector center bore 30 a and inflowselector spacer lumen 33, wherein one end of the placement cam 34 ismounted within the placement selector center bore 30 a and flush withthe flat surface of the placement selector 30 which is opposite thatwhich is in contact with the inflow selector spacer 32. In this positionit can be seen the long axis of the placement cam 34 is parallel to theaxis of the inflow spacer lumen 33 and placement selector fluid conduits31.

In FIG. 4 a the combined assembly of placement selector 30, inflowselector spacer 32, and placement cam 34 is depicted. In addition, theoutflow obturator 22 and the combined assembly of inflow obturator 20and inflow obturator spacer 24 is also shown. The combined assembly ofthe inflow obturator 20 and inflow obturator spacer 24 is depictedmounted on the placement cam 34 via the inflow obturator center bore 20a (shown in FIGS. 2 a-c). In FIG. 4 b the same components appearing inFIG. 4 a are shown. The combined assembly of the inflow obturator 20 andinflow obturator spacer 24 are shown at their final point of assemblymounted on the placement cam 34, wherein it can be seen the inflowobturator spacer lumen 33 accommodates the inflow selector spacer 32. Inaddition, the outflow obturator 22 is shown at its final point ofassembly mounted on placement cam 34 via the outflow obturator centerbore 22 a (shown in FIG. 2 d) at the opposite end of the placement cam34 as the inflow obturator 20, wherein the point of the cone-shapedoutflow obturator 22 points inward along the placement cam 34 toward theopposing point of the inflow obturator 20 similarly mounted on placementcam 34. FIG. 4 c depicts all the components shown in FIG. 4 b, with theaddition of the entire bellows structure 12 comprising the collectivegroup of structural members 10 (shown in FIGS. 1 a-c) which constitutethe bellows structure 12 (shown in FIGS. 1 a-c). The preferablycylindrically shaped bellows is positioned over the placement cam 34 sothat the center of the circular short-axis of the bellows issuperimposed over the same center point of the combined assembly of theinflow obturator 20, outflow obturator 22, inflow obturator spacer 24,inflow selector spacer 32, placement selector 30, and placement cam 34.Additionally, the bellows is placed longitudinally along the long axisof the placement cam 34 so that the longitudinal position of eachbellows structural member 10 (shown in FIGS. 1 a-c) is directly adjacentto that part of the placement cam 34 that is between the points of theopposing inflow obturator 20 and outflow obturator 22 mounted on theplacement cam 34. FIG. 4 c also depicts an example use of a skin 99which lines the bellows structure interior surface 16 (shown in FIGS. 1a-c) and which connects the bellows structure interior surface 16 withthe outside circumferential edges of the outflow obturator 22 and thecombined assembly of the inflow obturator 20 and inflow obturator spacer24, wherein the combination of the skin 99, outflow obturator 22, andinflow obturator 20 constitutes a definitive, airtight fluid chamber 18.

Now referring to FIG. 5 a, the combined assembly of the inventionincluding each of the components depicted in FIG. 4 c is shown. Inaddition, a generic inflow one-way valve 77 is shown attached to theplacement selector 30 and centered over the placement selector fluidconduits 31, thus providing an airtight cover over each of the placementselector fluid conduits 31. A similar generic outflow one-way valve 88is shown attached to the outflow obturator 22 and centered over theoutflow obturator fluid conduits 23, thus providing an airtight coverover each of the outflow obturator fluid conduits 23. The inflow one-wayvalve 77 will facilitate unidirectional flow through the placementselector fluid conduits 31 and inflow selector spacer lumen 33 in anantegrade direction toward the fluid chamber 18, while the outflowone-way valve 88 will facilitate unidirectional flow in the sameantegrade direction outward from the fluid chamber 18 and through theoutflow obturator fluid conduits 23. Thus retrograde fluid flow cannotoccur into the fluid chamber 18 from the outflow fluid conduits 23, orfrom the fluid chamber 18 through the inflow fluid conduits 21 towardthe inflow selector spacer lumen 33 and placement selector fluidconduits 31.

Accordingly, as previously described and in accordance with FIGS. 1 a-c,application of a compressing force onto the bellows structure willtransition the bellows from the inflated condition depicted in FIGS. 1 aand 5 a to the deflated condition depicted in FIGS. 1 c and 5 b, whichcauses a decrease in volume of the fluid chamber 18 contained by theskin 99 and bellows structure interior surface 16. Due to theaforementioned unidirectional fluid flow provided for by the inflowone-way valve, fluid contained in the fluid chamber 18 in the inflatedcondition of the invention (as shown in FIGS. 1 a and 5 a) will beejected from the fluid chamber 18, through the outflow obturator fluidconduits 23 and outflow one-way valve 88 as the volume of the fluidchamber 18 is reduced to the minimum associated with the deflatedcondition (as shown in FIGS. 1 c and 5 b). Particularly note that thepositioning of the inflow obturator 20 and outflow obturator 22 alongplacement cam 34 does not interfere or impede the range of travel of thebellows as it transitions from the inflated condition (as shown in FIGS.1 a and 5 a) to the deflated condition (as shown in FIGS. 1 c and 5 b).In the opposite fashion, as the volume of the fluid chamber 18re-expands into the inflated condition, fluid will flow antegrade intothe fluid chamber 18 from the inflow obturator fluid conduits 21 fromthe direction of the inflow one-way valve. Accordingly, repetitiveoperation of the bellows results in a fluid-pumping action whichprovides for operation of the invention.

In FIGS. 6 a-b the invention appears with all the components previouslyoutlined in FIG. 5 b. FIG. 6 b specifically demonstrates the result ofrotating the placement selector 30 in relation to the other componentsof the invention. The placement selector 30 is fixed to the placementcam 34, resulting in rotation of the placement cam 34 in relation to theinflow obturator 20 and outflow obturator 22. Since the inflow obturatorcenter bore 20 a is threaded in a fashion which mates with the threadsof the placement cam 34, rotation of the placement selector 30 causeslinear movement of the combined assembly of the inflow obturator 20 andinflow obturator spacer 24 to and fro along the placement cam 34.Comparing the relative location of the combined assembly of inflowobturator 20 and inflow obturator spacer 24 between FIGS. 6 a and 6 b,one can see the distance between the inflow obturator 20 and outflowobturator 22 within the fluid chamber 18 is shortened. Additionally, anew gap can be seen between the inflow obturator spacer 24 and theplacement selector 30, which exposes a portion of the outer surface ofthe inflow selector spacer 32 to view.

As previously described, application of a compressing force on thebellows results in a transition from the inflated condition toward thedeflated condition. However in FIG. 7 b, it can be seen the decreaseddistance between the inflow obturator 20 and outflow obturator 22 issufficiently less than the length of the bellows structural members 10(shown in FIGS. 1 a-c) to interfere with travel of the bellows to thefully deflated condition. It can be further seen that as the distancebetween the inflow obturator 20 and outflow obturator 22 continues to bereduced by further rotation of the placement selector 30, the degree ofbellows travel interference will increase further. Thus, rotation of theplacement selector 30 provides a direct means to control the maximumamount of volume capable of being displaced from the fluid chamber 18 ineach ventilatory cycle of the bellows.

In FIG. 8 a components of an example embodiment of a pressure restrictoris shown, comprising a ring-shaped or short-cylindrical outer housing40. Contained within the interior of the outer housing 40 is are twodisk-shaped stopper housings 41 which contains numerous housing fluidconduits 42 which permit fluid flow through the pressure restrictor.Encircling the outside surface of the outer housing 40 is a tube-shapedcontroller channel 44, which at one point empties into a pressurechannel 45. Within the controller channel an open-point stop 64 andclosed-point stop 65 can be seen as small projections which partiallyobstruct the lumen of the controller channel 44.

In FIG. 8 b a side view of the components depicted is FIG. 8 a isprovided. In this view it can be seen that a stopper notch 43 is cutaway from the interior of the outer housing 40. Adjacent to each side ofthe stopper notch 43 is a disk-shaped stopper housing 41, containingnumerous fluid conduits 42 which provide for a continuous fluidpassageway from one end of the lumen of the pressure restrictor outerhousing 40, though the fluid conduits 42 of one of the stopper housings41, through the area inside the stopper notch 43, through the oppositehousing fluid conduits 42, and out the opposite end of the outer housing40 of the pressure restrictor. Also seen in FIG. 8 b is a side view ofthe pressure channel 45 which communicates with the controller channel44, wherein the side of the outer housing 40 between the stopper notch43 and the end of the outer housing 40 which contains the pressurechannel 45 (the left side, as depicted in this view) constitutes theoutflow side of the pressure restrictor, while the opposite (or rightside, as depicted) side of the pressure restrictor constitutes theinflow side.

In FIG. 9 a-b a propeller-shaped stopper is depicted. The number ofblades of the stopper is identical to the number of stopper housingfluid conduits 42 (shown in FIG. 8 a-b), and are further related inshape to the shape of the housing fluid conduits 42, wherein the bladesof the stopper are shaped to provide variable coverage over the housingfluid conduits 42. The overall diameter of the stopper is related to thediameter of the stopper notch 43 of the outer housing 40 (both shown inFIG. 8 a-b), wherein the diameter of the stopper 50 is slightly lessthan the diameter of the stopper notch 43, whereby the stopper mayfreely rotate within the stopper notch 43. The thickness of the stopper50 is also related to the thickness of the stopper notch 43, wherein thethickness of the stopper 50 is slightly less than the thickness of thestopper notch 43, whereby the stopper 50 is contained within the stoppernotch 43 and may freely rotate within the stopper notch 43 withoutsubstantial to and fro play. Attached to the outer edge of one of thestopper blades is a pressure header spar 51, which supports a pressureheader 52. The shape and dimensions of the pressure header 52 is relatedto the internal shape and dimensions of the controller channel 44,whereby the shape and dimensions of the pressure header 52 allowsmovement within the controller channel 44 while also forming asubstantially airtight seal between the outer edge of the pressureheader 52 and the internal wall of the controller channel 44. Attachedto an outer edge of one of the stopper blades adjacent to that which isattached to the pressure header spar 51 is a controller header spar 53,which supports a controller header 54. The shape and dimensions of thecontroller header 54 is similarly related to the internal shape anddimensions of the controller channel 44, whereby the shape anddimensions of the controller header 54 allows movement within thecontroller channel 44 while also forming a substantially airtight sealbetween the outer edge of the controller header 54 and the internal wallof the controller channel 44.

In FIG. 10 a, a view of the combination stopper housing 41, housingfluid conduits 42 (shown subdued), and stopper 50 is provided. It can beseen that the stopper 50, contained inside the stopper notch 43 of theouter housing 40 (shown in FIG. 8 a-b) is sandwiched between two stopperhousings 41. It is also apparent in FIG. 10 a the rotational orientationof the stopper 50 in relation to the housing fluid conduits 42 of thestopper housing 41 is such that the stopper 50 fails to obstruct thehousing fluid conduits 42, which provides a means for fluid flow throughthe pressure restrictor.

Also depicted in FIG. 10 a are components of an example embodiment for acontroller, comprising a tube-shaped controller channel 44. Inside thecontroller channel 44 is a controller spring 60 which extends from itscontact with a controller lever 63 through the controller channel 44toward the opposite end of the controller channel 44, where thecontroller spring contacts the pressure header 52 which is alsocontained within the controller channel 44. The controller header 54 isalso shown contained within the controller channel 44, and morespecifically is in contact with the open-point stop 64. Accordingly, itcan be seen the controller spring 60, which is compressed within thecontroller channel 44, applies a force to the pressure header 52 in amanner which rotates the stopper 50 anti-clockwise until the controllerheader 54 comes into contact with the open-point stop 64. In thisconfiguration it can be seen the housing fluid conduits 42 areunobstructed, thus constituting an open condition of the pressurerestrictor.

In FIG. 10 b each component depicted in FIG. 10 a is shown, however itcan be seen the orientation of the stopper 50 is changed wherein thestopper 50 now obstructs the housing fluid conduits 42, whereby fluidflow through the pressure restrictor is interrupted. In addition, thecontroller header 54 is now seen to be in contact with the closed-pointstop 54, while the pressure header 52 continues to be in contact withthe controller spring 60. However, the overall volume of space insidethe controller channel 44 between the opening to the pressure channel 45and the pressure header 52 can be seen to be enlarged compared to thesame area depicted in FIG. 10 a. Accordingly, as pressure inside theoutflow side of the pressure restrictor increases, this pressure istransmitted through the pressure channel 45 into the controller channel44, where it exerts a force on the pressure header 52 which opposes theforce applied to the pressure header 52 by the controller spring 60.Thus, when the pressure in the outflow side of the pressure restrictoris sufficiently great enough to overcome the compressionary resistanceof the controller spring 60, the pressure header 52 will be pushedagainst the controller spring 60. Since the pressure header 52 isconnected, via the pressure header spar 51, to the stopper 50, thismovement causes the stopper 50 to rotate until the controller header 54comes into contact with the closed-point stop 65. When the pressureinside the outflow side of the pressure restrictor drops, the controllerspring 60 will return the pressure header 52, and thus the stopper 50,to the previous orientation depicted in FIG. 10 a. Thus, the degree ofpressure in the outflow side of the pressure restrictor directlycontrols opening and closing movement of the pressure restrictor.

In FIG. 11 a each of the components depicted in FIG. 10 a are depicted,however the position of the controller lever 63 within the controllerchannel 44 is seen to be changed, wherein the new position of thecontroller lever 63 provides for considerably greater compression of thecontroller spring 60 contained within the controller channel 44. Thiscauses the controller spring 60 to apply a greater force on the pressureheader 52, which will thus require a greater pressure in the outflowside of the pressure restrictor to result in further compression of thecontroller spring 60. Accordingly, movement of the controller lever 63provides an adjustable means to control the amount of pressure in theoutflow side of the pressure restrictor required to cycle the stopper 50between the open position and the closed position.

Thus it can be seen the example embodiment depicted provides severalfunctional and operational advantages over the prior art. As mentionedpreviously, one of the disadvantages of the prior art is the amount ofvolume generated by the device in each breath is highly unpredictable,making it difficult for the physician prescribing its use to anticipatethe degree of ventilatory support provided to the patient. In contrast,the bellows of the present invention along with the volume restrictorprovides a new ability to prescribe a specific tidal volume to bedelivered with each breath. As shown in FIGS. 1 a-c, application of acompressionary force to the outside of the bellows will result inuniform transition from the inflated condition to the deflated conditionwith complete disregard to any variability in operator technique,including whether one hand or two hands are used to squeeze the bellowsor the relative size of the hands of the operator. Additionally, even ifhand placement on the bellows is off-center, such as toward one end ofthe bellows rather than in the middle, the bellows will still compressdownward in a uniform movement since the coupling of the individualbellows structural members prevents the bellows from forming into anyacclivital or convoluted shapes. The ability to prescribe the exactvolume to be delivered to the patient in each breath will greatlycontribute to safety by avoiding patient exposure to excessive volumeswhich can contribute to lung injury, making a single version of theinvention suitable for use in patients of all age groups without theneed for redundant versions of different size designed for respectiveuse in adults, children, and infants. In addition, the definitiveadjustability of the invention ensures delivery of effective ventilatoryvolumes to maximize oxygenation and carbon dioxide removal.

A secondary benefit of this example embodiment of the invention is itsvisual resemblance to the prior art. Resuscitators are most oftenemployed during emergent life-saving efforts, and clinicians arereluctant to exacerbate the complexity of their tasks by experimentingwith new, unfamiliar devices substantially different from thosepresently in use, and in particular any pertaining to ventilation whichis to crucial to patient survival. The present invention effectivelyincorporates the desired functional attributes and improvements inclinical capability while substantially preserving utilizationtechniques predominantly in present use with the prior art, whichminimizes or even eliminates the need for retraining in artificialventilatory technique. Additionally, the invention incorporates asubstantially epicyclical design having no definitive top or bottom,which facilitates rapid and immediate commencement of artificialventilation without the need to orient the device into any specificposition or configuration.

A still further advantage of the present invention is the uniform andconsistent motion provided by the bellows also enhances versatility foruse in patients of variable age. In particular, it can be seen in FIGS.1 a-c that the height of the cross-section of the bellows depicted inFIG. 1 b is approximately one-half the height representative of thefully inflated condition depicted in FIG. 1 a, that is, the condition inFIG. 1 b is “half squeezed” toward the deflated condition. However, thevolume of the fluid chamber depicted in FIG. 1 b is substantially morethan half the total volume of the fluid chamber depicted in FIG. 1 a.Accordingly, a constant compressionary force applied to the bellows,resulting in a linear rate of decrease in the bellows cross-sectionaldimension, will be associated with a progressively increasing rate ofvolume displacement as the bellows progresses toward the deflatedcondition. This will result in an inherently low flow rate at thebeginning of a breath, with a slow and progressive increase in flow asthe breath nears the end of the inspiratory cycle. This “ramped” flowpattern has been previously described to result in improved air dynamicswithin the lung, and was previously clinically attainable only with theuse of complex, electromechanical ventilators. An additional benefit ofthis feature is that when smaller volumes are specified for use oninfants and children (who are more susceptible to lung injury), deliveryof the specified volume will require a relatively large amount ofbellows movement, thus the invention provides the benefit of moreprecise control when being used on these patients.

The combined use of the bellows and volume restrictor also provide someunique additional clinical benefits presently unobtainable with theprior art. Since the amount of gas ventilated to the patent in eachbreath is constant, the operator will perceive more uniform palpablelung resistance with the delivery of each ventilation. With moreexperienced operators, this may facilitate earlier suspicion oflife-threatening clinical conditions which are associated withprogressive perceived increases in lung resistance to ventilation.

The presence of a pressure restrictor as part of the invention alsoprovides for substantially improved clinical abilities. In infants andyoung children it is frequently desirable to use attainment of aspecific inspiratory pressure as an endpoint to the inspiratory cycle(i.e., ventilation is pressure-controlled) in place of delivery of aspecific volume with each breath (i.e., ventilation isvolume-controlled). Previous versions of the prior art have included apressure relief valve which vented excess pressure generated by theoperator to the atmosphere, however operation of these “pop-off” valvesoften interfered with delivery of effective ventilation. Alternatively,the pressure restrictor valve incorporated as part of the presentinvention provides the capability to restrict patient exposure topressures greater than a specific desired maximum by blocking outwardgas flow from the fluid chamber, rather than venting excess pressure tothe atmosphere. This important capability also enables the pressurerestrictor to be used in conjunction with the volume restrictor to allowclinicians to specify delivery of a specific volume (i.e., providevolume-controlled ventilation) to a patient while, to enhance safety,also specifying an upper limit to the airway pressure the patient is tobe exposed. Accordingly, if an operator squeezes sufficiently hard onthe bellows to exceed the maximum pressure, the pressure restrictor willtemporarily close, instantly cutting-off gas flow to the patient. As thelungs catch up and inspiratory pressure drops back below the maximumpressure, the pressure restrictor will reopen, allowing gas flow toresume until the pressure again exceeds the maximum. Depending on theforce applied by the operator, the pressure restrictor will rapidlycycle between open and closed conditions, providing a constant flow andpressure tempering or step-down function to effectively moderate airwaypressure exposed to the patient. This is particularly useful for use inunintubated patients, where patient exposure to airway pressures and gasflow rates even slightly higher than those required to ventilate thelungs rapidly results in diversion of gas into the stomach (gastricinsufflation)—a potentially life-threatening complication as previouslymentioned. Thus the invention provides a new ability for clinicians toemploy hyperventilatory techniques in intubated patients in completesafety, without the danger of causing iatrogenic lung injury associatedwith the prior art.

The combined use of both the volume restrictor and pressure restrictoralso provides a method to objectively monitor airway resistance. Duringvolume-controlled ventilation, the operator may progressively decreasethe pressure restrictor setting until the pressure restrictor interfereswith the complete delivery of the specified volume (i.e., the pressurerestrictor usurps control from the volume restrictor). At this point theoperator can determine from the pressure restrictor setting theapproximate airway pressure required to ventilate the specified volume,after which the pressure restrictor setting can be backed-off slightlyto again permit delivery of the full ventilatory volumes specified.Certain life-threatening intrathoracic injuries (e.g., collapsed lung,intrathoracic hemorrhage) are associated with progressively decreasingpulmonary compliance, which produces progressive increases in airwayresistance. Use of the invention in this manner will provide rapidclinical evidence of these conditions since the increase in lung airwayresistance will elevate pressures above the pressure restrictor setting.Sudden inability to deliver the specified volume will instantly alertthe operator to an increase in airway resistance, which will promptclinical reassessment of the patient's condition, enabling earlieridentification and treatment of the underlying cause. This technique canbe similarly be used to detect distal displacement of an endotrachealtube beyond the bifurcation of the trachea into the two mainstem bronchiwhich connect to each lung—airway resistance will increase if theoperator attempts to deliver a specific volume, previously provided toboth lungs, preferentially toward one lung.

A similar technique can also be employed during pressure-controlventilation to provide objective monitoring of pulmonary compliance. Thevolume selector can be tapered downward during pressure-controlventilation until the volume restrictor begins to usurp ventilatorycycling from the pressure restrictor, at which point the setting of thevolume selector can be observed to approximate the volume of gas beingaccepted by the patient's lungs for the given pressure restrictorsetting. The volume restrictor setting can then be backed-off slightlyallowing pressure-control ventilation to resume. If the operator wishesto reassess lung compliance, the volume restrictor is again tapereddownward to obtain another approximate determination of the volume ofgas being accepted by the patient's lungs for the given pressuresetting; any substantial decrease compared to the previous amount wouldbe indicative of decreased pulmonary compliance.

Although this description describes many specific components of theinvention, this should not be construed as a limitation of the scope ofthe invention but as merely providing an illustration of exampleembodiments of this invention. For example, an alternative volumerestrictor could have obturators which obstruct the bellows fromassuming a fully inflated condition as a means to restrict volume,rather than controlling volume delivered by preventing full deflation ofthe bellows. Thus the scope of the invention should be determined by theappended claims and their legal equivalents, rather than by the specificexamples provided in this specification.

1. A resuscitator with a variable output air flow rate, having acylindrical bellows including a latitudinal dimension and a longitudinaldimension, said bellows configured to contract latitudinally along saidlongitudinal dimension, said resuscitator comprising: a) output airvolume control means for adjusting permissible extent of latitudinalcontraction, said output air volume control means comprising: (i). afirst end piece insertable into said bellows at a first end; (ii). asecond end piece insertable into said bellows at a second end; and(iii). adjusting means for adjusting distance between said first endpiece and said second end piece.
 2. The Resuscitator of claim 1, whereinoutput air flow rate of said resuscitator increases as said bellows islatitudinally contracted uniformly along said longitudinal dimension. 3.The resuscitator of claim 1, wherein operation of said bellows ends at apreselected value of air flow rate.
 4. The resuscitator of claim 3,further comprising: (iv). regulator means for limiting air flow whensaid bellows is exerting pressure beyond a predetermined value.